Japanese pharmaceutical company Daiichi Sankyo has accused Malvinder Mohan Singh and Shivinder Mohan Singh of concealing and misrepresenting facts at the time of its $2.4-billion purchase of a controlling stake in Ranbaxy Laboratories in 2008 from the brothers. The accusation was made in an arbitration case filed in Singapore, said three people familiar with the development. Daiichi has sought compensation for losses arising from the $500-million settlement that Ranbaxy was forced to reach with the US Department of Justice in May over accusations that the company faked test results to get approval from the Food and Drug Administration for its medicines.